Do What Needs to Be Done Today.The secret of happy successful living is to do

what needs to be done now , and not worry about the past or the future.

Surveys Sampling

Simple random samplingRandom digit table

Representative Sample

(Simple) random sample: Each group of units of the required size from the population has the same chance to be the selected sample.

Human Being Bias

Please pick one number between 0 and 9 randomly.

** count # of students picking numbers 4,5,6 and show them the human being bias.

Resources of Random Numbers

Random digit table(p. 81 in Textbook)

Random numbers generated by computer software such as Minitab

(shown in lab)** Minitab: Calc >> Make Patterned >> Simple

Set of Numbers; and then Calc >> Random Data >> Sample from Columns

Example: Take 5 out of 300 randomly

Number the units in the population starting at 1 using the same number of digits (eg. 001, 002, …, 300)

In a random digit table, choose any number as the starting point, say row 2 column 3 (63753…)

From the starting point, read across the row 3-digit by 3-digit and get numbers from 001 to 300 to identify units

Example: 5 out of 300

From the table

63753 53067 79710 52555 72307 1022327475 10484 24616 13466…

3-digit numbers: 637, 535, 306, 779, 710, 525, 557, 230, 710, 223, 274, 751, 048, 424, 616, 134…

Random Assignments

Goal: Wish to assign 9 subjects to 3 treatments randomly.

Pick 1 out of 3 for each subject

Treatment assignments: 3, 3, 3, 1, 2, 2, 3, 2, 2